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Chapter 20: Q54P (page 984)

Draw the mechanism for the formation of β-lactose from a α- D-galactose and β- D-glucose in dil HCl.

Short Answer

Expert verified

Lactose, a disaccharide is a sugar made up of galactose and glucose subunits with the molecular formula C12H22O11. Lactose makes around 2-8% of milk. β-lactose is the beta anomer of lactose. It is a natural product found in Arisaema tortuosum and hypericum perforatum.

Step by step solution

01

Introduction

Lactose, a disaccharide is a sugar made up of galactose and glucose subunits with the molecular formula C12H22O11. Lactose makes around 2-8% of milk. β-lactose is the beta anomer of lactose. It is a natural product found in Arisaema tortuosum and hypericum perforatum.

02

Mechanism

As we can see that in the first step proton transfer occurs with HCl followed by the elimination of water. Now, nucleophilic addition of beta -D-glucose occurs at electrophilic carbonyl carbon of alpha-D-galactose. After this step occurs the deprotonation and thus, beta lactose is obtained. The raction mechanism can be represented as-

Mechanism of formation of β - lactose

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Most popular questions from this chapter

The disaccharide lactulose consists of a d-galactose pyranose subunit and a d-fructo furanose subunit joined by a b-1,4′-glycosidic linkage. After treatment of lactulose with

1. excess CH3I ,Ag2O ; 2 HCl,H2O, the d-galactose pyranose subunit was found to have one nonmethylated OH group, whereas the d-fructo furanose subunit had two. Draw the structure of α-lactulose.

Calculate the percentages of α-d-glucose and β-d-glucose present at equilibrium from the specific rotations of α-d-glucose, β-d-glucose, and the equilibrium mixture. Compare your values with those given in Section 20.10.

What are the systematic names of the following compounds? Indicate the configuration (R or S) of each asymmetric center.a. D-glucose b. D-mannose c. D-galactosed. L-glucose

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a. What sugar is the C-3 epimer of D-xylose?

b. What sugar is the C-5 epimer of D-allose?

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d. What sugar is the C-4 epimer of D-lyxose?
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